A. FIELD OF THE INVENTION
The technical field of the present invention is that of meltable smoke-producing pyrotechnic compositions with which any target can be camouflaged by impeding the transmission of the infrared radiation the target emits.
B. DESCRIPTION OF THE PRIOR ART
There currently exist few published works on the production of wide-band smoke screens, i.e. effective throughout the visible wavelengths down to the far infrared from 0.4 to 14 .mu.m.
Smoke-producing pyrotechnic compositions based on hexachloroethane as an oxidizer with zinc oxide as reducer are well known in the trade and as an illustration we can refer to U.S. Pat. No. 2,939,779. This type of composition produces a white screen that is ineffective against infrared detectors operating in the atmospheric windows of transparency, which are 3 to 5 .mu.m and 7 to 14 .mu.m.
The use of an aerosol of fine droplets or solid particles has already been proposed to stop infrared radiation. However, the resulting screens are very sensitive to the atmospheric conditions (wind and relative humidity in the case of metal cholorides) and they do not remain effective very long. As an example, we can refer to French Pat. No. 2,299,617 and French Pat. No. 2,309,828.
The French Pat. No. 2,560,186 is also known, which proposes a pyrotechnic composition for producing a smoke that is opaque to the infrared radiation from a target toward a heat sensor, wherein the smoke contains a component which, by thermal decomposition, generates particles of carbon ranging in size between 1 and 14 .mu.m, an oxidizer-reducer system reacting at a temperature above 1000.degree. C., and a binder.
This type of composition may include the following ternary system:
15 to 25 parts by weight of a metal powder, such as magnesium, PA0 15 to 85 parts by weight of hexachlorobenzene or hexachloroethane (oxidizer), PA0 0 to 30 parts of naphthalene (carbon generator). PA0 a reducer (most often magnesium powder) PA0 an oxidizer (hexachloroethane or hexachlorobenzene) PA0 a carbon generator (naphthalene, anthracene) PA0 a fluorinated binder (vinylidene polyfluoride). PA0 Hexachlorobenzene, because of its toxicity, is no longer commercially available on European markets. PA0 Aside from the manufacturing problems mentioned above, these compositions require mixing at least four components.
With the exception of the phosphorous that is cast to shape, but is ineffective in infrared, the smoke-producing compositions are usually powder mixtures formed under compression. These materials do not always offer the optimum mechanical properties, are difficult to machine for low compression ratios and are manufactured on a unit basis. The manufacturing process requires heavy equipment such as blenders, mixers, driers and presses that make it impossible to manufacture products of large dimensions. The fabrication process is complex and the unit price is high.
Furthermore, the smoke-producing pyrotechnic compositions used in producing a smoke screen against infrared radiation transmission include the following components:
These compositions exhibit two disadvantages: